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Full text of "Handbook Of Chemical Engineering - I"

102                               CHEMICAL ENGINEERING
Fixed charges:     (0.085 X 2,100).......................      $178.50
Labor charge:      (0.05   X 8 X 1,500)...................       600.00
Supply expense:  (0.02   X 5 X 1,500)...................       150.00
Power charge:     (0.03   X 5 X 1,500)...................       225.00
Depreciation:        (1.25   X280.2x|^)..............       210.15
$1,363.65 Net operating cost: (1,363.15/1,500 X 25).............................  $0.0363 per ton
Bucket carriers are a combination of a bucket elevator and a bucket conveyor in which the path of the buckets includes both elevating and conveying sections. The buckets are pan shaped and attached to two runs of endless chain. They may be attached rigidly to the chains, in which case the buckets are run through troughs on conveying stretches, dragging the load forward much like flight conveyors, or the buckets may be pivoted and suspended between the chains so that they maintain upright positions on both elevating and conveying stretches.
Rigid-bucket carriers discharge their load at points at which the buckets pass about sprockets from elevating to conveying stretches or through gates located in the bottom of the troughs on conveying runs. Pivoted bucket carriers discharge at any point along horizontal stretches of the conveyor by tilting devices which tip the buckets as they pass. Usually there are cams on either side of the buckets which engage a movable tripping cam set where desired.
Buckets are rectangular (depth equals width), pan-shaped, attached to matched endless chains in continuous succession or at regular spacings. The buckets of pivoted carriers are customarily mounted so that the edges of adjacent buckets overlap on horizontal runs, forming a continuous succession of buckets. Chains should be of the short link variety to avoid pulsations and intermittent motion in travel, though long-link chains can be used if compensating sprockets are employed.
Speeds for bucket carriers with rigid buckets may run as high as those employed for flight conveyors, but carriers with pivoted buckets should rarely be run at a speed greater than from 50 to 75 ft. per minute on account of the shock developed when dumping the buckets. Advisable speeds for pivoted bucket carriers when handling various materials are given in Table 12.
TABLE 12.—ECONOMIC SPEED OF BUCKET CARRIERS FOR VARIOUS   MATERIALS—
PIVOTED BUCKETS
SPEED, FEET MATERIAL                                                                                  PEK MINUTE
Coke...............................................:..          40
Broken stone (coarse)....................................           50
Lump coal—run of mine..................................           50
Ashes..................................................           60
Lime and cement........................................           60
Ore (average)...........................................           70
Crushed stone..........................................           70
Sand and gravel.........................................           70
Fine coal...............................................           80
The capacity of certain standard sizes of bucket carriers handling material weighing 100 Ib. per cubic foot and run at a speed of 50 ft. per minute is given in Table 13,